1. Field of the Invention
The present invention relates generally to foundations for movable dwellings, such as mobile homes and commercial coaches, and more particularly, to an improved pier for supporting a movable dwelling that substantially resists environmental forces, such as seismic and wind forces, and which includes means for anchoring the pier to a ground surface.
2. Description of Related Art
Movable dwellings, such as mobile homes and commercial coaches for example, typically comprise a prefabricated modular unit, that is somewhat longer than it is wide, to provide facile transportation of the unit. The unit is provided with a plurality of spatially positioned, elongated support girders or beams that extend parallel to the longitudinal axis of the unit. The support beams often have an "I" cross sectional configuration. A plurality of spatially positioned floor joists, that may have either a "J" or "C" cross sectional configuration, are supported by the beams and extend across the width of the unit. Additionally, some movable dwellings may incorporate a perimeter chassis with a beam having a "C" configuration.
Because these dwellings are movable, foundation systems incorporating piers are a preferable system for supporting the dwelling at an installation site, since the system can be disassembled if it is desired to move the dwelling. The piers are typically placed on a ground surface of the installation site and secured to beams of the unit, for supporting the unit. The piers are usually positioned beneath a beam, at an intersection of the beam and a joist, for example. The distance between the piers is usually governed by such factors as the dimensions of the unit and applicable building codes at the installation site of the unit.
Foundation piers in the prior art pier often comprise a base for supporting the pier on the ground of the installation site and a pair of opposing supports affixed to the base. The piers include suitable means for coupling adjustable extensions, affixed to the supports, to a beam of the unit. The coupling means may comprise a platform that abuts the beam and a pair of brackets, coupled to the platform. The coupling means are fastened to the desired beam, to secure the pier thereto.
A disadvantage of foundation piers for movable dwellings in the prior art, is that the coupling means is somewhat unstable due to the length of the shafts. A further disadvantage of these piers, is that when increased forces are applied to the pier, such as seismic activity and wind forces, the extensions may shear the bolts causing the pier to fail.
Another prior art foundation pier for supporting a movable dwelling, such as a mobile home or commercial coach, is disclosed in U.S. patent application Ser. No. 08/384,666, filed Feb. 6, 1995, now U.S. Pat. No. 5,595,366, wherein Applicant is one of the joint inventors. The pier disclosed therein includes a base having a threaded shaft, with a plurality of webs spatially positioned about the shaft. An adjustable support member has a first end threadably coupled to the shaft and couple members detachably coupled to a second end. The couple members attach the pier to a support beam of the movable dwelling, to prevent movement between the pier and the dwelling. A clamp member, affixed to the plurality of webs, couples to the support member for preventing relative movement between the support member shaft and clamp member. Environmental forces applied to the support member are transmitted from the clamp member and distributed through the plurality of webs to prevent the pier from collapsing.
A disadvantage of the disclosed pier, along with other piers in the prior art, is that the pier is not sufficiently secured to the ground. Piers, such as the pier disclosed in U.S. patent application Ser. No. 08/384,666, that are not secured to the ground are typically capable of withstanding approximately 1000 pounds of force. Since a movable dwelling that is approximately 24 feed wide, 60 feet long, and 10 feet tall is capable of generating approximately 12,000 pounds of force, due to wind forces for example, approximately 12 prior art piers must be used to in a foundation supporting such a dwelling. Thus, a pier that is capable withstanding greater force would be advantageous since less piers would be required to provided sufficient support in the foundation system.
However, it is known in the prior art to secure objects to the ground using various means. One particular means for securing a pier or other objects to the ground comprises an auger type device that screws into the ground. Augers suffer from a number of drawbacks, most notably that they extend a substantial distance into the ground, making them difficult to deploy, and that they do not always hold securely.
In a setting such as a mobile home park where a plurality of augers could be used to secure a foundation pier to the ground, subterranean utility connections may be damaged by the auger, when screwing the auger into the ground. Particularly, since the utility connections, such as electrical, gas, and water lines are buried from two to three feet beneath the surface and the auger is screwed into the ground up to approximately three feet in depth, the auger may potentially contact a buried utility connection, causing damage to the connection. Another disadvantage of augers, is that in soft or sandy soil the auger does not always provide a secure hold in the ground. This is due to the fact that the auger only engages an area of the ground as large as the diameter of the helical flange that extends about the auger's shaft.
Another known means for securing objects to the ground comprises a plurality of stake or rod members that extend into the ground and are coupled to a central plate or hub. One such means is disclosed in U.S. Pat. No. 5,243,795, to Roberts. The disclosed device comprises a tie down stake that is useful for anchoring small aircraft or other objects to the ground. The tie down stake consists of a central hub with an eyelet and a plurality of holes that serve as stake guides for directing a plurality of anchoring rods at a fixed angle downward and outward into the ground. The rods, joined by the hub, cooperate together to form a secure earth anchor.
U.S. Pat. No. 1,808,633, to Carver, discloses a ground anchor and like anchoring device. The disclosed device includes an anchor member having a plurality of wings radiating from the vertical axis thereof. Each wing has in its extreme corners, a pair of guides disposed one above the other. Stakes are adapted to be driven diagonally downwardly, so that each stake passes through an upper guide and then through a lower guide of the nearest possible opposite wing.
U.S. Pat. No. 5,039,256, to Gagliano, is directed to a pinned foundation system. The disclosed foundation system purportedly has resiliency under certain loading conditions and requires minimum excavation. The system has a cast footing in combination with a plurality of sleeves through which piles may be driven into the soil to create the necessary bearing, uplift, and lateral forces to support a structure. The sleeves are retained in a fixed position relative to the footing, at predetermined angles, corresponding to the specific structure loading characteristics desired for the ensuing foundation.
U.S. Pat. No. 2,870,884, to Mazur, discloses a ground anchor that converts horizontal pull into a vertical thrust. The anchor disclosed therein comprises a plate member adapted to rest on, and be supported by, the ground and to transfer forces over a relatively large area of the ground beneath the plate. The plate has a plurality of openings therein through which spikes or pins may be driven into the ground to hold the plate in place. Reinforcement members extending longitudinally of the plate and an attachment member to which a cable or chain is secured are additionally provided.
U.S. Pat. No. 4,052,827, to Yancey, discloses a ground anchor and foundation support, U.S. Pat. No. 3,788,335, to Hemmelsbach, discloses an anchor means for a portable building structure, and U.S. Pat. No. 3,937,436, to Stewart, discloses an anchoring apparatus.
While the above enumerated prior art references have improved features, they fail to disclose all of the advantageous features achieved by the improved seismic pier of the present invention that includes means for anchoring the pier to a ground surface.